Auto engineers have made great improvements in reducing injuries caused by frontal collisions. Airbags and seat belts work well. Also, the front of most vehicles contains the engine and the engine compartment, which can be designed to operate as a “crumple zone”. A crumple zone is a volume that absorbs at least a portion of the energy of a collision and lengthens the time of the collision event. The crumple zone presents a force in opposition to the collision force over a distance. By increasing the time of the collision event, and by absorbing a portion of the collision energy, the crumple zone reduces the G-forces on the vehicle occupants.
Rear collisions are a serious problem for small vehicles because the small vehicles do not have large trunk volumes comparable to the engine compartments. A small vehicle with a small trunk will offer little protection to the occupants when the vehicle is hit from the rear. Large vehicles typically have larger trunks, which can be designed to operate as an effective crumple zone.
Airbags are not useful in rear collisions because the occupants are in close contact with their seats. In a rear collision, the seats push on the bodies of the person in the seat. While there is some advantage to having the seats slide backwards in this situation, sliding seats is not an accepted practice because rear moving front seats could crush the legs of rear seat passengers.
With no crumple zone in the rear, the small vehicle exposes its passengers to very high G forces during rear collisions because motion of their bodies will change very rapidly. Force=Mass×Acceleration. The rapid velocity change of their bodies is a large acceleration and the resultant force on their bodies (masses) will be large. Also, a small vehicle will have a relatively small mass, and when it is hit in the rear by another vehicle while inert, the force from the collision on the low mass small vehicle will generate large accelerations, directly translating large accelerations and proportionally large forces on the passenger bodies.
Even if a passenger is constrained so that his body does not strike a hard surface, the high acceleration can tear internal organs and blood vessels. Similarly, the skull may move and compress and injure the brain.
Previous technology in this area has offered front, side and rear bumpers fixedly attached to springs in order to reduce damage to the vehicle from a collision. The springs may operate to absorb some of the force in a collision. Later technology had other shock absorbing devices that were placed between the bumpers and the vehicle. These devices were designed to dissipate some of the energy of the collision to reduce passenger injuries. Some of these devices allowed for the bumpers to be moved between multiple positions. These shock-absorbing devices were relatively small in volume, which limited the amount of energy they could absorb.
Side impact protection is a more difficult problem than frontal or rear impact protection. Vehicle sides do not traditionally have bumpers. The doors and side members of a conventional vehicle may be made from heavy gauge steel, heavier than other parts of the vehicle, in order to offer some protection for side collisions. The weight of this steel negatively affects the vehicle fuel economy.
Side airbags have been introduced to many vehicles. They are much narrower than the frontal airbags because the occupant's head is closer to the side of the vehicle than the steering wheel or dashboard. Closer proximity means that there is less time to absorb the energy of a side collision. Also, the side of a vehicle has much less steel between the passenger and an oncoming vehicle as compared to the front or rear of the vehicle and the passenger. Side collisions are much more deadly than frontal collisions.
Previous technology in this area has offered devices that were placed between the vehicle doors. They were designed to resist deformation of the vehicle chassis caused by a side collision. The devices did not extend beyond the sides of the vehicle and did not add to the side crumple distance.
Some other technology provides bumpers that remain in a retracted position until moments before an impending accident was detected. Then the bumpers would be rapidly extended. The detection of an impending accident is very difficult. There are many technologies that might be used to try to detect an impending collision, but they all suffer from the possibility of false alarms. A false alarm might injure a person who is next to the vehicle when the bumpers are deployed or cause property damage.
A bumper that can move and compress an energy absorbing material during a collision can significantly reduce the G-forces felt by passengers in a vehicle. There is, however, a problem with designing such a system. For a high-speed collision, a large volume of rigid energy absorbing material is needed. This is because of the large amount of collision energy to be absorbed. A lower speed collision may not generate enough force to begin compression of the energy absorbing material. If the large and rigid volume of energy absorbing material is not compressed during a lower speed collision, the energy absorbing material will provide no value during the lower speed collision. The vehicle passengers will feel the full G-forces that a rigid, fixed bumper would provide.
Gordon Murray is a famous British Car designer. He has recently suggested that cars designed for city driving should be designed to absorb lower speed crashes than cars designed for highways. This means that the city car is less safe on the highway because it will absorb less energy in a collision, and the passengers will suffer from higher G-forces.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.